1. Field of the Invention
The present invention relates generally to an optical transmission module for use in the optical communication field, and more particularly to a receptacle type optical transmission module.
2. Description of the Related Art
In the recent information communications field, high-speed large-capacity processing and high-speed data transmission are required in response to the advancement of information. To meet this requirement, optical transmission is indispensable and preparation is now proceeding toward the expansion and diffusion of an optical communications network.
Known as a device used at many sites in an optical transmission system is an optical transmission module having an optical circuit and an electrical circuit in combination for performing opto-electrical conversion or electro-optical conversion. At present, the production scale of the optical transmission module per communications maker is about 105 products per year. However, it is said that the production scale required in the future will become 106 or more products per year in response to the diffusion of an optical communications network and that the production cost must be reduced to about {fraction (1/10)} or less of the present level. Accordingly, it is strongly desired to establish any form of the optical transmission module which can realize mass production and low cost by minimizing the number of components to simplify the assembly process and can also ensure high reliability and long service life.
The components mounted on a printed wiring board built in a communications device are generally classified into a surface mount type and a through hole mount type. A typical example of the surface mount type components is an LSI, which has a form called a flat package. Such a component is soldered to the printed wiring board by a reflow soldering process. This process is performed by printing a solder paste on the printed wiring board, making the surface mount type component stick to the printed solder paste, and heating the whole in a conveyor oven to a solder surface temperature of 220xc2x0 C. or higher.
A typical example of the through hole mount type components is a large-capacity capacitor or a multi-terminal (200 or more terminals) LSI. The multi-terminal LSI has a terminals form called a PGA (Pin Grid Array). Such a through hole mount type component is soldered to the printed wiring board by a flow soldering process. This process is performed by inserting the terminals of the through hole mount type component into through holes of the printed wiring board, and putting the printed wiring board into a solder bath heated at about 260xc2x0 C. from the side opposite to its component mounting surface.
In mounting an optical module on the printed wiring board by soldering like the surface mount type component or the through hole mount type component, a so-called pigtail type of optical module with an optical fiber cord is not suitable as the optical module. That is, the optical fiber cord usually has a nylon coating, and the nylon coating has a low resistance to heat at about 80xc2x0 C., so that it is melted in the soldering step. Furthermore, the optical fiber cord itself invites inconveniences in accommodation and handling at a manufacturing location, causing a remarkable reduction in mounting efficiency to the printed wiring board.
Accordingly, to allow a soldering process for the optical module and reduce a manufacturing cost, the application of a so-called receptacle type of optical module is indispensable. An example of the receptacle type optical module allowing a soldering process is known from 1996 IEICE, General Meeting Proc., C-207 (Ref. 1). In Ref. 1, there is described a receptacle type optical module manufactured by retaining a photoelectric converter and a ferrule with a bare optical fiber on a silicon substrate, next covering the whole with a silicon cap to hermetically seal an optical coupling region, and finally molding the whole with an epoxy resin.
The silicon substrate is formed with a V groove for positioning the optical fiber and the ferrule, both of which are simultaneously fixed by the silicon cap. A lead frame is fixed by an adhesive directly to the silicon substrate, so that the lead frame forms electrical input and output terminals. A commercially available MU type connector housing is mounted on an optical fiber connecting portion to realize connection and disconnection of another optical fiber. By flow soldering of the lead frame extending from the molded package, the optical module is mounted on a printed wiring board.
Another example is known from 1997 IEICE, General Meeting Proc., C-361 (Ref. 2). In Ref. 2, a V groove for positioning a bare optical fiber and a ferrule is formed on a silicon substrate as in Ref. 1. The bare optical fiber is fixed to the silicon substrate by a glass plate through a UV curable adhesive, thereby realizing optical coupling between the optical fiber and a photoelectric converter.
An optical coupling region between the photoelectric converter and the optical fiber is sealed by a transparent epoxy resin. The silicon substrate is fixed to a lead frame forming an electrical input terminal, and the lead frame is connected through a gold wire to the photoelectric converter. The whole except an end portion of the ferrule is molded with a resin to form a molded package. An optical connector adapter is mounted onto the molded package to complete an optical module. The optical connector adapter is used to detachably connect another optical fiber to the optical module. By flow soldering of the lead frame extending from the molded package, the optical module is mounted on a printed wiring board.
In an optical subscriber transmission system, economization of the optical transmission system as a whole is also necessary. To this end, there has been proposed and standardized a wavelength division multiplexing bidirectional communication system having a single office terminal to be used commonly by many subscribers. To realize this configuration, an optical module having wavelength multiplexing/demultiplexing functions is required both in each of the subscriber terminals and in the office terminal. In particular, an optical module incorporating a PLC (planar lightwave circuit) formed by integrating the wavelength multiplexing/demultiplexing functions in one chip is expected from the viewpoints of mass production and cost reduction.
In reducing an assembly cost for such a subscriber optical transmission module, it is important to ensure a cost reducing technique for a receptacle structure of an optical fiber interface, especially, an interface between a PLC having wavelength multiplexing/demultiplexing functions and an optical fiber. Conventionally known is a self-alignment technique for the connection between a PLC and an optical fiber. In this conventional technique, a fiber guide is formed on a silicon substrate so as to make alignment of the core of an optical waveguide in the PLC and the core of the optical fiber, thereby determining optimum positions of the PLC and the optical fiber in a self-aligned fashion.
According to such a self-alignment mounting method, it is not necessary to supply a current to an optical semiconductor element, and it is also not necessary to provide a complicated aligning device for aligning the core of the optical waveguide and the core of the optical fiber. Further, no time for the alignment is needed. Accordingly, this method is suitable for mass production and cost reduction.
Known as another example of the receptacle type optical module in the prior art is a technique of optically connecting an optical element and a receptacle ferrule through a V-grooved silicon substrate in a self-aligned fashion. By replacing the optical element with an optical waveguide to follow this prior art technique, it is possible to obtain a structure such that the optical waveguide and the receptacle ferrule are to be optically connected through a V-grooved PLC substrate in a self-aligned fashion.
Also known as another prior art technique is a receptacle type optical module for providing an interface between a PLC having a plurality of optical waveguide cores and multiple optical fibers. In this prior art technique, V grooves for two guide pins are formed on a substrate, and optical coupling between a plurality of optical elements mounted on the substrate or the plurality of optical waveguide cores and the multiple optical fibers is attained through the two guide pins.
The above-mentioned conventional receptacle type optical module has the following problems. First, a deep V groove must be formed on the substrate, so as to mount the ferrule on the substrate. Accordingly, the silicon substrate on which the optical element is mounted or the PLC substrate on which the optical waveguide is formed must be made thick, resulting in an increase in material cost. Further, the substrate must be left under the ferrule, causing a disadvantage in reducing the thickness of the optical module.
Secondly, in the conventional receptacle type optical module, the ferrule mounted in the V groove and the optical element or the optical waveguide core are aligned with each other. Accordingly, there is a possibility of large misalignment between the optical waveguide core (or an active layer in the optical element) and the core of the optical fiber fixed in the ferrule, causing a large optical coupling loss. As a result, characteristics of the optical module are degraded.
It is therefore an object of the present invention to provide a receptacle type optical module suitable for cost reduction and size reduction.
It is another object of the present invention to provide a ferrule assembly required for assembling of the receptacle type optical module.
In accordance with an aspect of the present invention, there is provided a ferrule assembly comprising a ferrule having a through hole; and an optical fiber inserted and fixed in the through hole; the ferrule having a flat cut portion for semicylindrically exposing a part of the optical fiber inserted and fixed in the through hole.
In accordance with another aspect of the present invention, there is provided an optical module comprising a substrate having a groove; an optical waveguide layer formed on the substrate, the optical waveguide layer comprising an optical waveguide core having first and second ends, the first end being aligned with the groove, and an optical waveguide cladding covering the optical waveguide core; a ferrule having a through hole; and an optical fiber inserted and fixed in the through hole; the ferrule having a flat cut portion for semicylindrically exposing a part of the optical fiber inserted and fixed in the through hole; the ferrule being fixed at the flat cut portion to the substrate so that the part of the optical fiber exposed to the flat cut portion is inserted into the groove of the substrate until one end of the optical fiber abuts against the first end of the optical waveguide core.
Preferably, an optical element such as a laser diode or a photodiode is mounted on the substrate at its one end portion opposite to the other end portion on which the ferrule is mounted so that the optical element is optically coupled to the second end of the optical waveguide core.
In accordance with still another aspect of the present invention, there is provided an optical module comprising a substrate having first and second grooves at opposite end portions thereof; an optical waveguide layer formed on an intermediate portion of the substrate, the optical waveguide layer comprising an optical waveguide core having first and second ends respectively aligned with the first and second grooves, and an optical waveguide cladding covering the optical waveguide core; first and second ferrules each having a through hole; and first and second optical fibers inserted and fixed in the through holes of the first and second ferrules, respectively; the first and second ferrules respectively having first and second flat cut portions for semicylindrically exposing a part of the first optical fiber inserted and fixed in the through hole of the first ferrule and a part of the second optical fiber inserted and fixed in the through hole of the second ferrule, respectively; the first ferrule being fixed at the first flat cut portion to the substrate so that the part of the first optical fiber exposed to the first flat cut portion is inserted into the first groove of the substrate until one end of the first optical fiber abuts against the first end of the optical waveguide core; the second ferrule being fixed at the second flat cut portion to the substrate so that the part of the second optical fiber exposed to the second flat cut portion is inserted into the second groove of the substrate until one end of the second optical fiber abuts against the second end of the optical waveguide core.
In accordance with a further aspect of the present invention, there is provided an optical module comprising a substrate having a groove; an optical waveguide layer formed on the substrate, the optical waveguide layer comprising a first optical waveguide core having first and second ends, a second optical waveguide core having third and fourth ends, the third end being connected to an intermediate portion of the first optical waveguide core, and an optical waveguide cladding covering the first and second optical cores; an optical wavelength filter mounted on the substrate so as to intersect a junction between the first and second optical waveguide cores; a semicut ferrule assembly comprising a ferrule having a through hole, and an optical fiber inserted and fixed in the through hole, the ferrule having a flat cut portion for semicylindrically exposing a part of the optical fiber inserted and fixed in the through hole, the ferrule being fixed at the flat cut portion to the substrate so that the part of the optical fiber exposed to the flat cut portion is inserted into the groove of the substrate until one end of the optical fiber abuts against the first end of the first optical waveguide core; a first optical element mounted on the substrate so as to be optically coupled to the second end of the first optical waveguide core; and a second optical element mounted on the substrate so as to be optically coupled to the fourth end of the second optical waveguide core.
For example, the first optical element is a photodiode for detecting a laser beam having wavelengths in a 1.55 xcexcm band, and the second optical element is a laser diode for emitting a laser beam having wavelengths in a 1.3 xcexcm band.
In accordance with a further aspect of the present invention, there is provided an optical module comprising a substrate having a first maker at one end portion thereof; an optical waveguide layer formed on the substrate, the optical waveguide layer comprising an optical waveguide core and an optical waveguide cladding covering the optical waveguide core, the optical waveguide cladding having a narrow first portion and a wide second portion; a glass plate having a groove and a second marker, the glass plate being fixed to the substrate so that the second marker is aligned with the first marker, and that the groove accommodates the first portion of the optical waveguide cladding; and a semicut ferrule assembly comprising a ferrule having a through hole, and an optical fiber inserted and fixed in the through hole, the ferrule having a flat cut portion for semicylindrically exposing a part of the optical fiber inserted and fixed in the through hole, the ferrule being fixed at the flat cut portion to the glass plate so that the part of the optical fiber exposed to the flat cut portion is inserted in the groove of the glass plate to optically couple the optical fiber to the optical waveguide core.
In accordance with a further aspect of the present invention, there is provided an optical module comprising a substrate having a plurality of grooves; an optical waveguide layer formed on the substrate, the optical waveguide layer comprising a plurality of optical waveguide cores having a plurality of first ends respectively aligned with the grooves, and an optical waveguide cladding covering the optical waveguide cores; and a connector assembly comprising a block having a plurality of through holes, a plurality of optical fibers inserted and fixed in the through holes, respectively, and a plurality of guide pins fixed to the block, the block having a flat cut portion for semicylindrically exposing a part of each of the optical fibers inserted and fixed in the through holes; the block being fixed at the flat cut portion to the substrate so that the parts of the optical fibers exposed to the flat cut portion are inserted into the grooves of the substrate until front ends of the optical fibers abut against the first ends of the optical waveguide cores, respectively.
In accordance with a further aspect of the present invention, there is provided an optical module comprising a substrate having an end portion formed with a first groove and another end portion formed with a plurality of second grooves; an optical waveguide layer formed on an intermediate portion of the substrate, the optical waveguide layer comprising an optical waveguide core having a first end aligned with the first groove and a plurality of second ends respectively aligned with the second grooves, and an optical waveguide cladding covering the optical waveguide core; a first connector assembly comprising a first block having a first through hole, a first optical fiber inserted and fixed in the first through hole, and a plurality of first guide pins fixed to the first block, the first block having a first flat cut portion for semicylindrically exposing a part of the first optical fiber inserted and fixed in the first through hole; and a second connector assembly comprising a second block having a plurality of second through holes, a plurality of second optical fibers inserted and fixed in the second through holes, respectively, and a plurality of second guide pins fixed to the second block, the second block having a second flat cut portion for semicylindrically exposing a part of each of the second optical fibers inserted and fixed in the second through holes; the first connector assembly being fixed at the first flat cut portion to the substrate so that the part of the first optical fiber exposed to the first flat cut portion is inserted into the first groove of the substrate until a front end of the first optical fiber abuts against the first end of the optical waveguide core; the second connector assembly being fixed at the second flat cut portion to the substrate so that the parts of the second optical fibers exposed to the second flat cut portion are inserted into the second grooves of the substrate until front ends of the second optical fibers abut against the second ends of the optical waveguide cores, respectively.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.